For semiconductor microfabrication technologies, currently, 90 nm-level microfabrication has reached the practical stage, however, owing to the rapid sophistication of semiconductor devices in recent years, the importance in development of processing techniques in further microscopic nanoscales has been advocated. Under such circumstances, in Japan, the “Semiconductor MIRAI (Millennium Research for Advanced Information Technology) Project” was started as a national project in fiscal 2001 to work on development and practical use of 45 nm-level microfabrication as a target. In addition, at the private-sector level, the “ASUKA project” was started to work on development and practical use of 65 nm-level microfabrication as a target.
However, with regard to optical lithographic techniques by pattern transfer systems, which are currently the mainstream, despite the aim of higher precision by use of extreme ultraviolet radiation or X-rays for example, these have been approaching the limits in terms of high-precision mask formation, photoresist resolution, process control and the like.
In view of the problems as described above, the inventor of the present application has proposed, in Patent document 1, negative-type lithography for, without removing a natural oxide layer formed on a surface of a GaAs layer, by irradiating Ga ion beams onto this natural oxide layer, substituting either Ga2O3 or Ga2O for the oxide layer or generating either Ga2O3 or Ga2O on the oxide layer, followed by dry-etching the surface of the GaAs layer by use of a bromide for every single atomic layer.
According to this method, by using the natural oxide layer in place of a mask for the dry etching, it becomes unnecessary to form a special mask for the dry etching and also becomes unnecessary to remove the natural oxide layer. Furthermore, microindentations can be processed with an excellent shape and dimensional reproducibility.
Patent document 1: Japanese Published Unexamined Patent Application No. 2003-51488 (Paragraph number 0012, etc.).
Here, the resolution which has been conventionally used as a barometer of miniaturization does not indicate a resolution in a semiconductor itself to which a final processing whereby an original device function is expressed has been applied, but indicates a resolution after exposure on an organic resist that has been standardized in a lithographic process. The reason is that a large number of steps are required for the final processing to a semiconductor substrate in the conventional lithographic process, and the maximum resolution is determined depending on processing on the organic resist that is the first pattern transfer step. And, in actuality, a pattern fabricated on that organic resist itself is gradually transferred while involving “blurring” as a result of application of a plurality of post processes. In general, because this “blurring” is different depending on an objective processing method and material characteristics, it has been difficult to generally define the blurring. Accordingly, under the present circumstances, the resolution on the organic resist that has been standardized has been competed in the current lithographic process.